Color television transmission systems for elimination of cross modulation



United States Patent Inventor Appl. No.

Filed Patented Assignee Priority Satoshi Shimada Tokyo, Japan 712,530

March 12,1968 Dec. 15, 1970 Sony Corporation Tokyo, Japan a corporationof Japan March 13.1967 Japan COLOR TELEVISION TRANSMISSION SYSTEMS FORELIMINATION OF CROSS MODULATION 5.6, 5.8; 332/40, 48; l79/l5ACS, 15;325/156, 157, 154, 139,5.8A

Attorneys-Albert C. Johnston, Robert E. lsner, Lewis H.

Eslinger and Alvin Sinderbrand ABSTRACT: A novel color TV transmitter isprovided having at least two modulators for modulating a video carrierwith the FM sound signal, modulated chrominance signal, and luminancesignal. The outputs of the at least two modulators are combined to makeup the composite transmitted signal. In one embodiment, a combined FMsound signal and luminance signal is applied to one modulator, while themodulated chrominance signal is applied to the other modulator. In afurther embodiment, the FM sound signal is applied to one modulator, anda combined luminance signal and modulated chrominance signal is appliedto the other modulator. ln certain embodiments, the outputs from the atleast two modulators are combined in an adder circuit, while in othersthey are combined in a differential circuit. Still further embodimentsare shown. The system of the transmitter avoids beat noise, cross talk,and intermodulation.

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Satan; hi Ski maria COLOR TELEVISION TRANSMISSION SYSTEMS FORELIMINATION OF CROSS MODULATION This invention relates to a new andimproved transmitter system for use in color television, and moreparticularly to a simplified but stable transmitter for a plurality ofinformation signals including a subcarrier signal.

In color television of, for example, the NTSC system, the I differencein frequency between a sound carrier wave 1'. and picture carrier wavef, must be held constantly and precisely at 4.5 MHz. For this purpose,conventional types of transmitters specially employ an oscillator such,for example, as a stable but expensive crystal oscillator of 4.5 MHz.,which effects the so-called frequency control for maintaining thefrequency difference exactly at 4.5 MHz. This introduces drawbacks suchas complexity in construction and expensiveness in the manufacture oftransmitters and further intermodulation of a sound modulation carrierand another modulation carrier leads to generation of heat noises. As aresult of this, crosstalk is caused and the beat noises are likely to bereproduced in a monitoring picture.

Accordingly, it is a principal object of this invention to provide a newand improved transmission system for color television signals or thelike. V

It is a further object of this invention to provide a new and improvedtransmitter for a plurality of modulation signals.

It is another object of this invention to provide a new and improvedtransmission system for color television signals which have no beatnoises between modulated signals.

It is another object of this invention to provide a new and improvedtransmitter in which a modulation index of input signals may beincreased easily.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The organizationand manner of operation of this invention, together with further objectsand advantages thereof, may best be understood by reference to thefollowing description-taken in connection with the accompanyingdrawings, in which:

FIGS. 1 and 2 are block diagrams illustrating examples of a conventionaltransmission system for color television signals;

FIG. 3 is a block diagram, for explaining a transmission system forcolor television signals according to this invention;

FIGS. 4 to 6 are similar block diagrams showing other modified forms ofthis invention; and

FIG. 7 illustrates circuit connections of the principal circuits of thetransmission system exemplified in FIG. 5.

In FIG. 1 there is illustrated in block form one example of the priorart color television signal transmitter. The transmitter comprises asource of a sound signal S and a frequency modulator l in which acarrier frequency f,,, is modulated by the sound signal. Further, thetransmitter includes sources of a luminance signal Y, a chrominancesignal C and a balanced modulator 2 in which a subcarrier frequency f.,,of 3.58 MHz. produced by. for example, a crystal oscillator 6 ismodulated by the chrominance signal C.

The chrominance signal C includes color difference signals, for example.red and blue difference signals R-Y and B-Y, which are respectivelyapplied to the balanced modulator 2. The luminance signal Y and asubcarrier f modulated by the balanced modulator 2 are supplied to anadder 4 respectively. The output I of the adder 4 is applied to anamplitude modulator to which a carrier wave f of VHF frequency is alsofed from an oscillator 8. The output 1} of the frequency modulator andthe output I, of the amplitude modulator 5 are respectively applied toan adder 3, the output signals of which are transmitted and radiated byan antenna. With the prior art transmitter it is necessary to holdexactly the frequency difference between 1,, and f at 4.5 MHz.

FIG. 2 shows another example of the prior art transmitter, in which amodulated sound signal 1}, having a center frequency of 4.5 MHz., aluminance signal Y and a chrominance signal I, modulated by a balancedmodulator 2 are applied together to an adder 4a, the output of which is,in turn, fed to a final amplitude modulator 7. Reference numeralssimilar to those in FIG. 1 indicate similar elements and the operationof this transmitter is the same as that of the above example. Hence, nodetailed description will be repeated. In the transmitter of FIG. 2,both the sound signal and chrominance signal are modulated in the finalamplitude modulator 7, and therefore beat noise is likely to occur dueto frequency difference of 920 kHz. present between f,, and IConsequently, during receiving the signal, the so-called crosstalk maybe caused and beat noises are displayed in a monitoring picture.

FIGS. 3 to 6 illustrate examples of a novel and improved transmitteraccording to this invention which is free from the drawbacks describedabove. In the following examples of this invention similar elements areidentified by similar reference numerals.

The transmitter exemplified in FIG. 3 comprises a plurality ofmodulators 5a, 5b and 5c to which a common carrier wave f is appliedrespectively from a single oscillator 8. A sound signal S modulated by afrequency modulator la, a luminance signal Y and a chrominance signal f,modulated by a balanced modulator 2, which are the same :as thosedescribed with FIGS. 1 and 2, are respectively fed to the amplitudemodulators 5a, 5b and 5c. The outputs of the modulators 5a, 5b and 5care applied together to an adder 3a and the resultant signal areradiated through an antenna. This invention does not causeintennodulation, because the sound signal S and the subcarrierchrominance signal f are applied to the modulators 5a and 50independently of each other. This ensures avoidance of heat noisegeneration and/or crosstalk. Further, slight variations of the carrierwave f are permissible, because the frequency difference of 4.5 MHz. isconstantly maintained by the modulator la. This permits simplificationof the transmitter and reduction of the cost thereof.

FIG. 4 shows another example of the transmitter according to thisinvention, in which the modulated sound signal f is combined with theluminance signal Y at the adder 4b. The output of the adder 4b andmodulated chrominance signal f modulated at the balanced modulator 2 arerespectively applied to the amplitude modulators 5d and 5c. The circuitarrangement on the right of the broken line lV-IV in the FIG. isidentical with that on the right of the line IlI-llI in FIG. 3.

FIG. 5 illustrates a further example of this invention, which isidentical with those exemplified in FIGS. 3 and 4 except in that theluminance signal Y and the modulated chrominance signal f are fedtogether to an adder 4a.

In the example depicted in FIG. 4 the output signals e, and e, of theamplitude modulators 5d and 5c are added together by the adder 3a in theform of its output 6w: The equation of this operation is given asfollows:

where A and? are constants, Y(t) a hfriinarice signal @65- ponent, C(!)a chrominance signal component, 8(1) a sound signal component and top aphase angle of the carrier wave. It must be noted that the modulationindexes of the luminance signal and the sound signal and that of thechrominance signal are reduced to and respec- In this case the polarityof sound signal are respectively enhanced up to the chrominance signalcomponent is inverted as indicated by and B**C(b8and this indicates a180 phase shift of the subcarrier of the color subcarrier but is notrelated to the information content of the chrominance signal. A circuitfor providing the 180 phase shift may be included either in the balancemodulator such as by adding a phase shifting transformer or a transistoramplifier of the common emitter configuration.

The foregoing examples have been described with the main carrier wave ofVHF but it may be of UHF FIG. 7 illustrates concrete circuit connectionsof the circuits In, 5a, 52. 3a and 8 of the transmitter shown in FIG. 5.The operation of the transmitter can be readily understood. and hencethe following brief description will be given. The sound signal from theamplifier for sound signal is applied through an inductor CH1 to the 4.5MHZ. FM modulator 1a to a common point between a grounded variablecapacitor diode, VD and capacitor C4; capacitor VD and C4 are shuntconnected with two series connected capacitors C2 and C3. The junctionof capacitor C2 and C4 is connected to a tank circuit made up of C5 andone winding of a transformer. This junction point is also connected to acollector of a transistor X1 which has its emitter connected to a commonpoint of capacitor C2 and C3. A resistor R3 is also connected betweenthe emitter and ground. Divider resistors R1 and R2 are seriallyconnected between power source +1 2v. and ground, and have their commonpoint connected to a base of transistor X1 and through a capacitor C1 toground. The output of the modulator oscillator is applied through atransformer, one winding of which is in the tank circuit with thecapacitor C5. The output signal is 'applldto'an emitter followeramplifier through another winding of. the transformer and a capacitor C6and then to the base of a transistor X2. Two divider resistors R5 and R4are connected serially between the +l2v. source and ground, with acommon point at a base of the transistor X2. A collector of thetransistor X2 is connected to the +1 2v. power. A load resistor R6 isconnected to an emitter of transistor X2 and to ground; and the output,namely the FM modulated sound signal is tapped off this load resistor R6and is applied to an Am modulator 5a.

The combined luminance and modulated chrominance signal are applied froman adder 4a to a second AM modulator 5e which is similar to the AMmodulator 5a.

1 The second input to both modulators 5a and Se is the video signalcarrier shown here coming from VHF oscillator 8. The oscillator has atransistor X6 and a crystal frequency source XTAL connected between itsbase and ground. Divider resistors R14 and R15 are connected betweenground and a tuned circuit made up of capacitor C and one winding of anoutput transformer. A common point between the resistors is connected tothe transistors base; and a common point between the tuned circuit'scapacitor and winding is connected to a collector of the transistor. Acapacitor C19 is connected between a collector and an emitter oftransistor X6 and capacitor C18 is connected between the emitter andshunted by a resistor R16. The common point of the tuned circuit andresistor R15 is connected through an inductor CH2 to the +l2v. source.inductance CH2 passes a DC component from the supply to the oscillatorand blocks the high frequency signals of the oscillator from passinginto the power supply. The output of VHF oscillator 8 is applied througha transformer and capacitors C16 and C17 respectively to modulator 5aandmodulator 5e. It might be noted that the phase of the signal appliedto modulator 5a is different than the phase of the signal applied tomodulator 5e. However. in the adder circuit 3a to which the signals aresubsequently applied, an equal and opposite amount of phase differenceis put back into the signals. so that the finally produced output signalhas the improper phase relationship.

Referring now to modulator 5a. it will be recalled that the output fromthe FM modulator la is applied to the modulator 5a. Modulator 50consists of a transistor X3. dividing resistors R7 and R8 connectedbetween the source of potential +l2v. and ground. with their commonpoint at a base of the transistor X3. Bias-temperature compensationresistor R9 is connected between the emitter and ground, and a passcapacitor C8 is also connected in shunt with the resistor R9. The FMsound signal is applied through a capacitor C7 to the base of thetransistor and the VHF oscillations from oscillator 8 is also applied tothe base of the transistor. The capacitance of C7 is such that the VHFsignal does not pass therethrough; and the capacitor C16 in the outputof the VHF oscillator is such that the FM signal is blocked thereby. Thecombined signals are thus applied to the transistor X3 which modulatesand amplifies them and provides the output at its collector. A tunedcoupling transformer made up of a transformer and capacitors C9 and C 10passes the output signal from the modulator to the adder 3a.

The second AM modulator, 5e, receives the input signals from the VHFoscillator 8 and the combined luminance and modulated chrominance signalfrom the adder 4a. The latter signal is applied through an emitterfollower amplifier. The emitter follower is made up of a transistor X4having its base connected to receive the combined signals from adder 4a.A load resistor R10 is connected between an emitter of transistor X4 andground, and a collector is connected to the +1 2v. source. The outputfrom the emitter follower shown in the drawing as an arrow having alegend flis applied to the modulator 5e.

Modulator Se is made up of a transistor X5 and is biased (in a fashionsimilar to that of transistor X3 in modulator 50) by divider resistorsR12 and R11. Emitter resistor R13 and pass capacitor C12 are connectedbetween an emitter of transistor X5 and ground. The video carrier inputis applied from oscillator 8 to a base of transistor X5 and the combinedluminance and modulated chrominance signal is applied to the emitter oftransistor X5. The input signals are modulated by the transistor and themodulated output is taken from the collector through a tune circuitmakeup of transformer and capacitor C13 and C14 and applied to addercircuit 3a. Power is provided from the +1 2v. source, shunted bycapacitor e11, to the collector of transistor X5 through one winding ofthe output transformer and to one terminal of the bias resistor R12.

The outputs from modulator 5a and 5e are applied to adder circuit 3awhich is a transformer shown having a split primary winding one half ofwhich receives the output from modulator 5a and the other receiving theoutput from modulator 5e. It will be noted that there is a phasereversal ofone signal which corresponds to the phase reversal of theoutput of the VHF signal from oscillator 8. The combined signals appearon a secondary winding of the transformer and is passed through acoupling capacitor C15 to the output. The numerical values of thecircuit components in one preferred embodiment of the transmitter are asfollows:

Voltage 12 volts Capacitors:

pf 20 C3 pf 50 C4 pf 50 C5 pf C pf 1, 000 C7 ..!lf 0. 01

C3 llf..

Cg pf C 0 pf C11 I-lf C12 pf..

C 3 pf v C 4 pf C 5 pf (1, pf means for incorporating said luminancesignal with the C -pf-- 15 modulated signals so that the output from thecombining C18 -P 10 circuit includes the carrier modulated with thesound,

g chrominance, and luminance signals. gg f 5 2. A system according toclaim 1 wherein the means for in- RI 8 corporating the luminance signalis still another modulator R d 75 connected to the carrier source, andadapted to receive the lu- R; do--- 1 minance signal, for modulating thevideo carrier with the lu- 4 10 minance signal; and said modulator isconnected to the comg: -gg- 2 l0 bining circuit wherein the modulatedluminance signal is combined with the other signals received by thecombining circuit. 3. A system according to claim 1 wherein the meansfor in- R0 1 corporating the luminance signal is an adder circuitconnected R d 1 between the FM modulator and said one modulator forreceivd0 5. 6 l5 ing the FM modulated sound signals from the FMmodulator, i2 and for also receiving the luminance signal, and combininge 8kg:- 2 g said:l signals and providing the combined signal to said onemo ulator. g3::::::::::':::::':':""32:" 4. A system according to claim Iwherein said means for in- Inductors; 20 corporating the luminancesignal includes an adder circuit 1 ,,H 100 connected between thebalanced modulator and the other QH -pH- 100 modulator for receiving themodulated chrominance signal Transistors: and the luminance signal andcombining the received signals X1, X4 and providing the combined signalsto said other modulator. Diode: I 51 A system according to claim 3wherein the combining cir- VD (variable capacitor) 18353 cult IS anadder circuit, and the output therefrom has the form:

It will be apparent that many modifications and variations may beeffected without departing from the scope of the novel concepts of thisinvention.

lclaim:

l. A transmitter system for a color video signal comprising:

an FM modulator adapted to receive a sound signal and modulate it on asound carrier;

a balance modulator adapted to receive color difference signals andmodulate them on a chrominance carrier;

, a source of video carrier;

a pair of modulators connected to the carrier source, one beingconnected to the FM modulator and the other being connected to thebalanced modulator, for respectively receiving the modulated signalstherefrom and modulating the video carrier with the modulated signals;

a combining circuit connected to the pair of modulators for receivingthe video carrier modulated signals therefrom and combining said signalsto provide a combined output signal;

+ -SU) sin (wpt) wherein A and B are constants Y(t) is the luminancesignal, C(t) is the chrominance signal, S(t) is the sound signal, and

WP is a phase angle.

